This invention relates to an improved process for making integral skin polyurethane using a blowing agent comprising, in its simplest form, a carbonate or bicarbonate source with or without water. This blowing agent is combined with an isocyanate source, a polyol source and/or a third stream, and the polyol source, a polyurethane catalyst, the blowing agent and the isocyanate source are mixed and reacted to form a polyurethane material with a foamed interior and a tougher, more densely packed, outer skin layer that is formed integrally with the interior. The polyol source and/or third stream may be compounded with cross-linking agents, chain extenders, fillers, pigments, fire-retardants, UV-absorbers and the like.
It is well known that polyurethane may be prepared by the reaction of a polyisocyanate and a polyol in a closed mold. One type of polyurethane polymer include polyurethane compounds with foamed interiors and more compact integral outer skin layers. Compounds of this type, known as integral skin polyurethanes, are quite common and may be used to make a variety of products. Such compounds resemble vinyl or synthetic leather and are commonly used, for example, to make products such as arm rests and dashboards in automobiles.
In the past, integral skin polyurethane has been made from a polyisocyanate and a polyol using a catalyst to promote the reaction and FREON 11 halogenated hydrocarbons as the blowing agent which foams the polyurethane during the polymerization. Cross-linking agents, coloring agents, surfactants and/or plasticizers are frequently added to the mixture depending on the final product to be produced from the integral skin polyurethane. Although this technique for making integral skin polyurethane has previously worked well, environmental regulations have been passed and are now in place which prohibit the use of FREON 11 agent in the making of integral skin polyurethane. This has caused many manufacturers to change to FREON 141B halogenated hydrocarbon. However, this compound too will soon be banned as an environmental hazard. Pentane is an alternative compound which could be used as a blowing agent in the making of integral skin polyurethane. However, pentane is extremely volatile and highly flammable and therefore potentially quite dangerous. For this reason, the use of pentane as the blowing agent presents challenging safety problems.
This invention provides a solution to the problem of finding a safe, environmentally acceptable yet effective blowing agent for use in the process of making integral skin polyurethane materials. In particular, a carbonate source, such as baking powder or soda, with or without water can be used effectively as the blowing agent instead of FREON agents or pentane compounds to produce high quality integral skin polyurethane. Moreover, by using a bicarbonate source such as baking soda as the blowing agent, existing integral skin polyurethane molds and molding techniques and methods can be used.
It is, therefore, a principal object of this invention to provide an improved process for making integral skin polyurethane which can be carried out without using a FREON agent or pentane compound as the blowing agent.
It is a further object of this invention to provide an improved process for making integral skin polyurethane which uses a carbonate or bicarbonate, optionally with water, as the blowing agent.